Combustible gas detector



March 4, 1958 J. A. DALEY, JR; ET AL V, 2

COMBUS' IIBLE GAS DETECTOR I Filed Aug. 25, 1954 2 Sheets-Sheet 2 INVENTOR.

2,5 5? @645/ f-. BY My 17 in I7 9 United States (estimate Times, US. Code(1952 sec 266) The invention" described herein may be "manufactured and.used"by5or5for the Government of he Un'itedfS of America for" governmental purposes without the ay ment of any royalties thereon or therefor. I i

This rinve'ntion concerned with 'me art "ordevices for measuring the combustibility of gas mixtures; T

In'thefmany' fields "of" industrial' endeavor including research, production andtransportation, there arises quite often-an environment that i's'capa'ble of being dangerous 1 to men; mater'ialsand' equipment due to'the presence of a gas mixture which is potentially "combustibleor' ex explosive. -'Such situati0ns'may arise where fuels arebe' ingiproduced", transported; developed or evaluated,""or when devicesusingfuels.are primarily'involved. Such} dangeroussituationsnlay inifac't arise whenever any f sort of -explosiye or' corribu'stible gas or volatile liquid isf being utilized for any purpose whatsoever. An added" complication exists ii'n --that quite often in normally f safe environments there maybe a-su'dden build up oreven a gradual build-upto a-danger point of 'gas mixtures con-'- taining= these dangerous gases. In the absence of anaccurate means to detect" the presence of such gasesfthe personnelgin'such an environment tm'ay' be unaware of their situation and willfail --to takeuproperprecautions or willeven actually do something tov explodeorig-"- nite them. On the other hand; the 'provision'of a sirn 40 p1e,-'durable device which will detect these dangerous gasesrwould have a large-- number; of applications and would-considerably enhance the safety of such environf ments s r r l w 1' The prior art methods fo'r this purpose have "involved""4 the use of catalytic combustion devices and methods't'; which depend upon the variable thermal conductivity of diif'er'ent concentrations of gaseous mixtures. 'The 'in-r-i strument utilized in the catalytic combustion method;r'e-f quires ,acatalyticfilament. Thistype of instrument has" a value only in a limited range of gas mixtures and it is intended primarily for use 'only in the zero to lower ex plosive limit range. Otherdisadvantages 'aretha't when the filament is exposed to combustible mixtures -fo'rsa T long periodnof .time,: the instrument has a tendency to zero [drift and contact'withrichmixtures considerably reducesithe-life of the filamentp- The devices which in? volvethe thermal conductivity method must be carefully i screened and proper operation of the instrument requires a knowledge of the gas composition; c :6

This inventionwhich avoids the defects of, the prior bustible gas mixture is one which can be; utilized inall ranges of concentration, and has no parts of short life,-;i:.

nor does 'it require careful handling and operation. Ourdevice makes use of the temperature rise of gas after a combustion 'process. The temperature rise in a combustion process is a function of the heating value'ofthe i1 fuel, the.design of the. combustion chamber and the concentration of the, mixture The heating values-fol? con-r temporary fuels arevery nearly constant. The com--1 bustion chamber design isv governed not'onlyby-the idei tures whic'h utili s of ameans for carrying out :the 'metho'doutlinedf'above ing and indicating means canbe 'set up .toroperate percan meter through-anorifice-onothersuitable means 6 2 sired shapeof the charhber but also by the pressure level" and velocity head of the mixture. With a properly designed combustion chamber'the velocity head and shape of the chamber can be-controlled so as to yield a constant value'of combustion efiiciency. If the pressurelevel and/oritie mperature of the sample gas are very much ditferent' from atmospheric, it is proposed to condition" atmospheric conditions'Thus the tembs l t j o i 9 I a "hs ntan'e'ously' indicate the con 7 e in terms 'of its lower and/( f hr in he'alternatiye indicate whether ple, rugged and durable device for the combustion of gas mixtnrs s that-their cb'mbustibility'may be determined. 'It is stillanoth bjec of this invention to provide-fa deVice fOr deter ning the' combustibility of gas mixthe;heating value of a' gas mixture asa -measur'e of its cornb'ustibility; a

'It is -a further' obj'ect' of th s invention to provide a devicefor' determiningthe cornbustibility of a gas mix f ture whichautiliies the temperature rise when a gas s ampleis'i'burried-to thereby ascertain its heating value and combustibility; f f

It' is'a still further object of this'invehtiOntdifdvide an apparatus :rfor: bu'rn'in'ga a sample "'gas" mixture aiid" measuring the temperature rise wh'ereby its combustibilit'y may:be' determii'redta 1 These .and othere objects" and many'of the 'attendan advantages "ofthis invention will ibe readily apprecia "d' as, the; samewbecomes better understood by reference the 1 following detailed description? when considered' "in connection with the accompanying drawings wherei 'Figure 1 is a block diagram of the "entire" device.

Figure 2 is v an isometric view"of' the burner assembly Figure 3 is asidewiewrih -crosssection of the huriie assembly.

In-Figure -1' thereris shown a "schemativpi'esentatio The-;manner and elements ofthdmean's which". ar'e to be"used-in--'a *given instance depend upon theexplosive rangeof' the gas mixture and it will be found that in a' given situation one-range willbe *present'andthe detectmanentlyacoording to the needs of the particular range The; complete device; comprises of a'burner assembl 1 which is described'in greater detail'below. A spark plug or other, Suitab1e igniti0n means 2 is rriountedonrF- the burner and is supplied by a source of electrical en ci ergy as at Inserted/into thecombustion m'eansrl JiSTfi thermocouple 4 which detects 'the -temperature"increase: 5 during a combustion process. A fuel or sample mixture; supply-5 is connectedito fthe-burrier by conduit 6 and a measured quantity of fuel. Anair or sample supply f mixture 7 'is' also connected to the burner 1 by conduit-8 and can meter-byrneans'of the orifice or other suitable means 8' ameasuredjquantit'y of air or sample mixture, methodsja'nd devices .for sensing and indicating a com-*2 1 ation isf as follows: A measured.quantitfofgffll from the reservoir 5 is added to a known qu'an'tityp'f the". mixturewhich it is desir'e d totest and"vvhiclrma held forusein the-air reservoirj. This rjesu bustible mixture whi-ch is-"ig'ni'ted 'n 'thejhiirne "rue It-is aiiotherbbjecfioflthis invention to provideasun 3 bustion are cooled with a known quantity of the gas mixture being tested and the difference in temperature of the original sample gas mixture and the temperature of the mixture of fuel and gas sample after combustion cooled by the additional sample gas is detected by the.

wall 12 and end wall 14 forming a chamber 16. The side thermocouple 4 and presented .on the. indicator 9. The

indicator may be calibrated in any manner for presenting the desired information. It has been found con venient to calibrate it from to 100% of explosive.

that some very small percentage of the coolant sample mixture is burnt and the sensitivity of the device is thereby increased.

Thetmethod of operation of the to high explosive range is as follows: A known quantity of the sample gas is burned in the combustion chamber and is cooled with a known quantity of air containing no gas mixture. before combustion and after combustion and cooling by the air is detected by the. thermocouple 4 and transmitted tothe indicator which may be calibratedas set 1 out above. The air in this: instance is added only to prevent excessive temperatures in the combustiondevice. In analyzing gas mixture above the high explosive The temperature rise of the sample gas system in the lower wall 12 has a partially threaded passage 18 formed therein which receives the threaded bushing 18' to connect and position conduit 8 to the housing. The end 14 is formed with a threaded passage 20 which receives the threaded bushing 22 connecting and properly positioning the conduit 6 in the housing. Mounted in the housing 10 is mixing chamber 24 which has a hole 26 in one "end communicating with the end of the conduit 6 and holes 28 in its side which communicate with the chamber 16 and thereby the conduit 8 through the passage 18. The chamber 24 has a flange, 30 formed on one end thereofa Formed on the interior of the wall 14 is a boss 32 on which is mounted the spring 34 which abuts the flange 30 at its other end. The spring functions to properly positionthe chamber 24 in the housing when the combustion device is assembled. Mounted in the interior of theqchamber 24 is :a diffuser 36 formed of a rigid porous material which is held in position by the shoulder means 38 and aids" in the mixing of gas and air or gas on the mixing chamber housing 10 by means of a plu limit a known quantity of the sample gas is mixed with 1 a known quantity of air of zero gas concentration, the air being added since the gas mixture itself does not contain sutficient oxygen to support combustion. This mixture of gas and air is cooled after combustion with 1 another known quantity of air, again to prevent excessive temperature rise, and the temperature detected and indicated.

The apparatus, therefore, remains basically the same under the three difierent range conditions, it is only the air; fuel and sample mixtures in tanks 5 and 7 that are altered. It is contemplated that in the first range (the zero to the lower explosive range), tank 5 contains fuel while tank 7 contains only the sample mixture. In the medium range, either the sample mixture only is used for both cooling and burning and is stored in tank 7,

or the sample mixture is stored in tank 5 for combustion purposes only and cooling air. is stored in tank 7 for cooling purposes. While in the high explosive range, either tank 5 accommodates a sample mixture together with a fixed quantity of air and tank 7 stores air for cooling. only, or the samplemixture is in tank 5 and the air kept in tank 7 is used for both cooling and bummg.

In each of the above ranges, a basic calibration must be made within the specific range with known sample mixtures. In each range of testing, the only unknown is the sample mixture content or percentage combustibility, as the amount'of fuel added, the amount of air added, the cooling effect etc. are all known or fixed quantities. H j

Thus it is seen that there has been described' a device and method for the sensing and indicating ofjthe'con'centration of gas mixtures in terms of their explosive limits.

The apparatus and basic method are the same for all ranges and vary as explained above according to the needs of the particular range.

2 and 3. Designated generally by reference lithe-burner assembly comprises two parts, a mixing chamberhousing 10 and a combustion chamber housing 40.

The housing 10 is in the form of a cylinder with a side rality of bolts 42. Provided in the far end of the housing '40 is an aperture 44 whereby the products of c0mbustion may escape. The combustion chamber is formed of two parts, a main portion 46 and a head portion 48. This is done for ease of fabricationand assembly. A shoulder means 50 aids in the proper positioning of the chamber :in the housing.- It can be seen that when the housing 40 is assembled on the housing 10 with the chambers 24 and 46 inside the spring 34 pushing against the flange 30 exerts a force holding all the elements in their proper assembled position.

Passing through hole 52 in the main chamber portion 46, ahole 54 in the housing 40 and held in position by the threaded bushing 71 is the thermocouple 4 which extends into the path of the gases being burned. A plurality of small holes 56 are formed around the peripher'y of the chamber for a purpose to be described below. The spark plugs 2 are threaded into the housing as at 58 and extend into the chamber 46 through holes formed therein. The combustion chamber is formed to achieve optimum combustion and has a hole 60 communicating with the interior of the diffuser. The outer diameter of the combustion chamber is less than the inner diameter of the housing 40, leaving an annular passage 62 whereby gas and/or air can be admitted through the holes 56 to the interior of the chamber.

Tanks 5 and 7 are connected to conduits 6 and 8 which in turn are joined to passages 26 and 18 respectively. Meter means 6 and 8 are inserted in lines 6 and 8 and measure the flow therethrough. The meters are conven' tional rate controlling meters of the rotor meter type, whichmeters contain a conventional st0p-cock to control the flow. Since such meters are conventional, they have been illustrated diagrammatically.

In the operation of the system the burner functions as follows: When operated in the low "range fuel. passes through conduit 6, the metering means 6' and the hole 26 into the interior of the mixing chamber. The sample mixture passes through conduit 8, metering means 8 and holes 28 to the interior of the mixing chamber where it is mixed with the incoming fuel and is further mixed bythe action of the diffuser 36 through which both the fuel and mixt-ure'pass. The fuel and mixture then pass through" the passage 60 into the combustion chamber where they'are ignited by the spark plugs 2. Meanwhile some portion of the sample mixture passes from the chamber 16; through the annular passage 62 and through the hol'es-f56whereinit serves as the known quantity of sample ir'nixtiire" added after, combustion. The known :qua'ntity isfdeterminedbecausejthe' dimensions of the various passages in the lower assembly are known and the flow therethrough can be calculated. This of course is done beforehand and is taken into consideration in the calibration of the temperature indicator.

Since the amount of fuel added, the amount of cooling action occurring, and the amount of sample mixture added are known factors, the only unknown is the percent concentration. Upon combustion, a temperature will be reached which will correspond with some known calibration temperature. Since the temperature indicator is calibrated in percent concentration, a visual means is provided for fast, accurate determination of the concentration of gas mixture in terms of its explosive qualities.

When the device, on the other hand, is used in the middle range of explosive concentration, two difierent methods, but both basically similar, may be used. In the first method, the sample mixture is entrained in tank 7 and the fuel is cut off from tank 5. A portion of the sample mixture, consequently, enters the combustion chamber via ports 18, 28, through the filter 36 and passage 60; at the same time, the remainder of the mixture enters into the combustion chamber via passage 62 and ports 56 to cool the combustion products just before the temperature indicator.

The second method in the middle range has a sample mixture in tank and air in tank 7. Only the sample mixture is burned in the combustion chamber as ports 28 are blocked ofi by plugs such as is shown by plug 70 of Fig. 3. As a result, the air is used solely for cooling purposes. After burning in the combustion chamber, the products of combustion are cooled by the air and the temperature of the air and combustion products is recorded on the indicator.

In the final or high range of concentration, two hasically identical methods are also available. In the first, the set-up is the same as the latter set-up in the middle range, i. e. the air and sample mixture set-up. In this case, however, the ports 28 are unblocked and the air p-artakes in the combustion process after mixing with the sample mixture in the difluser 36 and the associated passage.

The second method in the high range of concentration has a fixed quantity of air and a sample mixture in tank 5, air alone in tank 7, and the ports 28 blocked. The mixed air and sample mixture from tank 5 passes through the rate meter and diffuser and burns in the combustion chamber. The combustion products are cooled by the air entering the chamber through ports 56.

From the foregoing it can be seen that there has been provided a simple device having no parts subject to wearing out which can be used in the method we have provided for the sensing and measuring of combustible gases. I

Obviously many modifications and variation of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A burner assembly comprising a housing, means comprising a first chamber within said housing, means comprising a mixing chamber located within said first chamber means, combustion chamber means within said housing, said combustion chamber being connected to said mixing chamber, by-pass conduit means joining said first chamber and the combustion chamber, means to add fuel into the mixing chamber, connecting means between the first chamber and the mixing chanmber, and means to add a sample gas mixture into said first chamber whereby the mixing chamber.

2. A burner assembly comprising a housing, mean comprising a first chamber Within said housing, means comprising a mixing chamber located within said first chamber means, combustion chamber means within said housing, said combustion chamber being connected to said mixing chamber, by-pass conduit means joining said first chamber and the combustion chamber, means to add a sample gas mixture into saidmixing chamber and combustion chamber, means to burn said gas in the combustion chamber and means to add a cooling gas into said first chamber whereby said cooling gas enters the combustion chamber via said by-pass means to cool the products of combustion therein.

3. A burner assembly comprising a housing, means comprising a first chamber within said housing, means comprising a mixing chamber located within said first chamber means, combustion chamber means within said housing, said combustion chamber being connected to said mixing chamber, by-pass conduit means joining said first chamber and the combustion chamber, said mixing chamber and first chamber having a passageway therebetween connecting the mixing chamber and the first chamber, means to add a gas into said first chamber, said gas flowing into said mixing chamber and burning in said combustion chamber, and also passing through said bypass means into the combustion chamber to cool the products of combustion, and means to record the temperature of the mixture of the products of combustion and the cooling gas.

4. A burner assembly comprising a housing, means comprising a first chamber within said housing, means comprising a mixing chamber located within said first chamber means, combustion chamber means within said housing, said combustion chamber being connected to said mixing chamber, by-pass conduit means joining said first chamber and the combustion chamber, said mixing chamber and first chamber having a passageway therebetween connecting the two chambers, means to add a sample gas mixture into said mixing chamber, means to add a second gas into said first chamber, and means to ignite the new mixture of gas and sample gas mixture.

5. A burner assembly comprising a housing, means comprising a first chamber within said housing, means comprising a mixing chamber located within said first chamber means, combustion chamber means within said housing, said combustion chamber being connected to said mixing chamber, bypass conduit means joining said first chamber and the combustion chamber, said mixing chamber and first chamber having a passageway there-v between connecting the two chambers, means to control the fiow through said passageway, means to add a fluid comprising at least a sample gas mixture into said mixing chamber, and means to add a gas into said first chamher, said second gas entering at least the by-pass conduit.

References Cited in the file of this patent UNITED STATES PATENTS 1,625,277 Packard Apr. 19, 1927 1,827,930 Bissell Oct. 20, 1931 2,001,114 Schmidt May 14, 1935 2,083,521 Miller June 8, 1937 2,329,459 Dickey Sept. 14, 1943 2,349,517 Pinkerton May 23, 1944 2,586,899 Yanikoski Feb. 26, 1952 

